'Preventive genetics' for healthier Holsteins

by Jeff Stuart

ealthier Holsteins could be the products of "preventive genetics," a breeding system being developed by U of G researchers to enhance the immune response and disease resistance of dairy cows.

Prof. Bonnie Mallard, Pathobiology, is developing a selective breeding system that holds promise for providing healthier cows that can produce more milk of higher quality. Mallard, along with fellow pathobiology professors Bruce Wilkie and the late Bri an Kennedy, has already shown the benefits of breeding for better health in pigs.

The researchers have designed a program that uses blood and skin tests to measure the immune responses of young pigs. Those animals with enhanced immune function were bred, and the results have proved rewarding. The healthier pigs grow faster and reach market weight more quickly.

"We have shown with pigs that it is possible to select for health-related traits," says Mallard. "It may be that the high-immune-response pigs are healthier and can therefore devote more energy to growing."

Healthier animals also require fewer antibiotics, an important consideration for farmers wishing to market their products to increasingly health-conscious consumers.

Mallard is trying to bring these strategies that have worked with pigs to the dairy industry. She and M.Sc. student Laurie Wagter are testing the same skin and blood parameters developed for pigs to identify high-immune-response cows, with promising e arly results. Now they are trying to take this one step further by identifying the genes responsible for enhanced immune response or disease resistance.

Mallard and PhD student Shayan Sharif are studying a family of genes called the major histocompatability complex (MHC). These genes are responsible for making critical proteins involved in the immune response. They have identified one 'bad' gene that a ppears to be associated with an increased incidence of mastitis, an inflammation of the mammary glands in dairy cows that causes a reduction in milk quantity and quality and results in significant losses to dairy producers.

Mallard is now trying to determine if the genetic marker is associated with impaired immune function. It may also be possible to identify genes that are responsible for enhanced immune response. Eventually, good and bad genes (like the one they've alre ady found) may be identified in young calves, permitting a more informed selection of animals for further breeding.

In time, information on the different immune responses and the presence of specific MHC genes may be pooled to give an "estimated breeding value," which provides an indication of overall Holstein health.

"As we learn more about what makes dairy cattle healthier," says Mallard, "we can make increasingly more informed choices in the breeding process, so that we can consistently identify the healthier animals. We believe this will increase herd production and reduce the cost of looking after the cows. When viewed across the entire industry, the financial gains of these improvements could be quite significant."

This research is sponsored by the Natural Sciences and Engineering Research Council, the Ontario Ministry of Agriculture, Food and Rural Affairs and SEMEX.